In many situations it is desirable and/or necessary to analyze the network path through which packets travel from a sending point to a receiving point in the network. For example, when telephone conversation is transmitted over an IP network using Voice over IP protocol (VOIP) the jitter and delay introduced by the network affect the quality of the conversation as perceived by the users.
The following discussion will use the terms “near end” and “far end”. As the terms are used herein, the “near end” is the network end point from which action is being initiated. The far end is the network end point that transmits packets to the near. The near end may be an endpoint at which a technician is located. However, a near end may also be an end point that a technician can control from a remote location, or an near end may be a network end point at which an action is automatically initiated.
Various methods are described in the prior art for analyzing the path between the end points of a network. Three such prior art techniques are described below.
A method in which “No-op” packets are used to analyze a media path in a packet switched network is described in the first co-pending application referenced above. The no-op packets are Real Time Protocol (RTP) payload packets that contain no media content. A Real Time Control Protocol (RTCP) report is generated for the received RTP no-op packets. A marker bit is set in one or more of the no-op packets that triggers the no-op packet receiver to send back the RTCP report. The operation of the media path is determined by examining the statistics in the RTCP report. For ease of reference, hereinafter the technique described in the first co-pending application listed above will be referred to as the “no-op technique”
Another technique that can be used to identify problems in Internet Protocol (IP) networks is what is known as User Datagram Protocol (UDP) traceroute. The UDP traceroute makes special use of the IP Time To Live (TTL) field which is a part of IP packets. With this technique the TTL value in the traceroute packet can be varied to isolate a trouble spot in the IP network. One problem with the UDP traceroute technique is that it is not effective in detecting network problems for IP media streams. This is because the UDP traceroute packets do not necessarily travel along the media path used by the IP media stream.
Still another technique that can be used to analyze a path in a network is described in the second co-pending patent application referenced above. With the method described in the second co-pending application listed above, media packets are sent with modified Time To Live (TTL) values to intentionally cause rejection of the media packets at intermediate nodes in a media path. Rejection notices caused by the TTL modified media packets are then analyzed to isolate Quality of Service (QoS) problems in the media path. For convenience of reference, the technique described in the second co-pending application listed above will be referred to as the “variable TTL technique”.
From the viewpoint of a particular network end point, a network has a “near end” and a “far end”. As used herein the terms “near” and “far” do not necessarily refer to physical distance.
The present invention is directed to technique for analyzing the path used by incoming packets at a near end of a network. It is noted that using the no-op technique described in the first co-pending application listed above, involves sending packets from one location to a second location to analyze a path. Thus, from the point of view of a technician trying to analyze the path used by incoming packets, the no-op technique requires that packets be sent from the far end of the network. In some situations a technician may not have access to the far end of a network.